Injection pen with dial back and last dose control

ABSTRACT

A medication injection pen comprises a dose set knob rotatable with respect to a housing to set a desired injection dose. The dose set knob comprises at least one internal thread. A leadscrew includes a thread element for advancing in a first direction via a corresponding thread engagement. A driver is rotationally fixed to the leadscrew and is rotatable in a first direction to rotate and advance the leadscrew in the first direction. The setback member is rotationally fixed to the driver. The dose stop member is rotationally coupled to the setback member and is axially movable relative to the dose set knob when the dose set knob is rotated relative to the setback member. Axial movement of the dose stop member limits the user from setting a dose that is greater than an injectable volume of medication remaining in a cartridge.

RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 15,669,349, filed on Aug. 4, 2017, which is a division of U.S.Nonprovisional Application Ser. No. 13/261,300, fled on Jul. 27, 2012,which is a U.S. national stage application under 35 U.S.C. § 371 ofInternational Application No. PCT/US10/003059, filed Nov. 30, 2010,which claims the benefit of U.S. Provisional Patent Application Ser. No.61/265,562, filed on Dec. 1, 2009, and Ser. No. 61/351,465, filed onJun. 4, 2010, each of which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The present application relates to multi-dose medication injection pendevices with improved functionality, including improved dial-back of aset dose, and improved last dose control.

BACKGROUND OF THE INVENTION

Various medication injection pen devices are known in the prior an.These prior art devices sometimes include features for enabling a userto correct a dose that has been set too large, which may be referred toas “dial back”. Another feature that may be provided by some of theprior art devices is the ability to control a last dose of a medicationcartridge such that a user cannot set a dose greater than the remainingamount of medication in the cartridge. This feature is referred to aslast dose control or last dose management. Both of these features aredesired by users of such pen devices; however, the prior art devices donot satisfactorily meet these needs. Many prior art devices may provideone of these features, but not both. Further, many of the prior artdevices require additional steps for performing dial back, which arecumbersome and not intuitive to the user. Thus, there is a need in theart to provide improved functionality of dial back and last dose controlmechanisms together in a medication injection pen.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention address at least theabove problems and/or disadvantages and provide at least the advantagesdescribed below.

Accordingly, a first exemplary embodiment of the present inventionprovides a medication injection pen comprising a housing, for housing adose set knob, a leadscrew, a driver, a setback member, and a dose stopmember. The dose set knob is rotatable with respect to said housing toset a desired injection dose, and comprises at least one internalthread. The leadscrew includes a thread element by which it isadvanceable in a first direction via a corresponding thread engagement,said first direction being that which expels medication from acartridge. The driver is rotationally fixed to said leadscrew forpreventing relative rotation therebetween, said driver being rotatablein a first direction to rotate and advance said leadscrew in said firstdirection. The setback member is rotationally fixed to said driver forpreventing relative rotation therebetween. The dose stop member isrotationally fixed to said setback member and comprises an externalthread in threaded engagement with said internal thread of said dose setknob, said dose stop member being axially movable relative to said doseset knob when said dose set knob is rotated relative to said setbackmember, and wherein axial movement of said dose stop member limits theuser from setting a dose that is greater than an injectable volume ofmedication remaining in the cartridge.

According to another exemplary embodiment of the present invention amedication injection pen is provided comprising a housing, for housing adose set knob, a leadscrew, a driver, a setback member, and a dose stopmember. The dose set knob is rotatable with respect to said housing toset a desired injection dose. The leadscrew includes a thread element bywhich it is advanceable in a first direction via a corresponding threadengagement, said first direction being that which expels medication froma cartridge. The driver is rotationally fixed to said leadscrew forpreventing relative rotation therebetween, said driver being rotatablein a first direction to rotate and advance said leadscrew in said firstdirection. The setback member is rotationally fixed to said driver forpreventing relative rotation therebetween, and is provided with anexternal thread thereon. The dose stop member is rotationally fixed tosaid dose set knob and comprises an internal thread in threadedengagement with said external thread of said setback member, said dosestop member being axially movable relative to said dose set knob whensaid dose set knob is rotated relative to said setback member, andwherein axial movement of said dose stop member limits a user fromsetting a dose that is greater than an injectable volume of medicationremaining in the cartridge.

According to yet another exemplary embodiment of the present invention amedication injection pen is provided comprising a housing, for housing adose set knob, a leadscrew, a driver, a setback member, and a dose stopmember. The dose set knob is rotatable with respect to said housing toset a desired injection dose. The leadscrew includes a thread element bywhich it is advanceable in a first direction via a corresponding threadengagement, said first direction being that which expels medication froma cartridge. The driver is rotationally fixed to said leadscrew forpreventing relative rotation therebetween, said driver being rotatablein a first direction to rotate and advance said leadscrew in said firstdirection. The setback member is rotationally fixed to said driver forpreventing relative rotation therebetween. The dose stop member isrotationally fixed to said dose set knob and comprises an internalthread in threaded engagement with said thread of said leadscrew, saiddose stop member being axially movable relative to said dose set knobwhen said dose set knob is rotated relative to said setback member, andwherein axial movement of said dose stop member limits a user fromsetting a dose that is greater than an injectable volume of medicationremaining in the cartridge.

According to yet another exemplary embodiment of the present invention amedication injection pen is provided comprising a housing, for housing adose set knob, a leadscrew, a driver, a setback member, and a clickelement. The dose set knob is rotatable with respect to said housing toset a desired injection dose. The leadscrew includes a thread element bywhich it is advanceable in a first direction via a corresponding threadengagement, said first direction being that which expels medication froma cartridge. The driver is rotationally fixed to said leadscrew forpreventing relative rotation therebetween, said driver being rotatablein a first direction to rotate and advance said leadscrew in said firstdirection. The setback member is rotationally fixed to said driver forpreventing relative rotation therebetween. The click element ispositioned between said dose set knob and said setback member, saidclick element comprising a first arm member engaging an internal surfaceof said dose set knob, and a second arm member engaging an externalsurface of said setback member, wherein one of the said first and secondarms produces an audible signal when said dose set knob is rotated withrespect to said housing.

According to yet another exemplary embodiment of the present invention amedication injection pen is provided comprising a housing, for housing adose set knob, a leadscrew, a driver, and a setback member. The dose setknob is rotatable with respect to said housing to set a desiredinjection dose. The leadscrew includes a thread element by which it isadvanceable in a first direction via a corresponding thread engagement,said first direction being that which expels medication from acartridge. The driver is rotationally fixed to said leadscrew forpreventing relative rotation therebetween, said driver being rotatablein a first direction to rotate and advance said leadscrew in said firstdirection. The setback member is rotationally fixed to said driver forpreventing relative rotation therebetween. The housing further comprisesa flexible protrusion provided on a surface within said housing, and thedose set knob further comprises a flexible tab element which engagessaid protrusion to produce an audible signal upon completion ofinjection of a set dose.

Additional objects, advantages and salient features of exemplaryembodiments of the invention will become apparent to those skilled inthe art from the following detailed description, which, taken inconjunction with annexed drawings, discloses exemplary embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other exemplary features and advantages of certainexemplary embodiments of the present invention will become more apparentfrom the following description of certain exemplary embodiments thereofwhen taken in conjunction with the accompanying drawings, in which:

FIG. 1 depicts a medication injection pen according to an exemplaryembodiment of the present invention;

FIGS. 2A and 2B depict unassembled and assembled cross-sectional views,respectively, of exemplary components provided in a medication injectionpen according to a first exemplary embodiment of the present invention;

FIG. 2C depicts an unassembled view of a pen needle usable in exemplaryembodiments of the present invention;

FIGS. 3A and 3B depict views of a body provided in a medicationinjection pen according to the first exemplary embodiment of the presentinvention;

FIGS. 4A and 4B depict views of a dose set knob provided in a medicationinjection pen according to the first exemplary embodiment of the presentinvention;

FIGS. 3A and 5B depict views of a setback member provided in amedication injection pen according to the first exemplary embodiment ofthe present invention;

FIGS. 6A and 6B depict views of a click element provided in a medicationinjection pen according to the first exemplary embodiment of the presentinvention;

FIG. 7 depicts a view of a driver and leadscrew arrangement provided ina medication injection pen according to the first exemplary embodimentof the present invention;

FIGS. 8A and 8B depict views of a dose stop member provided in amedication injection pen according to the first exemplary embodiment ofthe present invention;

FIGS. 9A and 9B depict views or a leadscrew brake provided in amedication injection pen according to the first exemplary embodiment ofthe present invention;

FIGS. 10A and 10B depict views of an alternative injection couplingmechanism provided in a medication injection pen according to the firstexemplary embodiment of the present invention;

FIGS. 11A-11F depict views of alternative leadscrew brake and threadedinsert embodiments provided in a medication injection pen according tothe first exemplary embodiment of the present invention;

FIGS. 12A-12E depict views of an end-of-injection click mechanism in amedication injection pen according to the first exemplary embodiment ofthe present invention;

FIG. 13 depicts a view of a muted injection click mechanism in amedication injection pen according to the first exemplary embodiment ofthe present invention;

FIGS. 14A and 14B depict views of an additional mechanism for reducingfriction between components in a medication injection pen according tothe first exemplary embodiment of the present invention;

FIGS. 15A and 158 depict exemplary mechanisms for connecting a cartridgeto a medication injection pen according to the first exemplaryembodiment of the present invention;

FIGS. 16A and 16B depict unassembled and assembled cross-sectionalviews, respectively, of exemplary components provided in a medicationinjection pen according to a second exemplary embodiment of the presentinvention;

FIG. 17 depicts a view of a driver and leadscrew arrangement provided ina medication injection pen according to the second exemplary embodimentof the present invention;

FIG. 18 depicts a view of a last dose control mechanism provided in amedication injection pen according to the second exemplary embodiment ofthe present invention;

FIGS. 19A and 19B depict views of alternative last dose controlmechanisms provided in a medication injection pen according to thesecond exemplary embodiment of the present invention;

FIG. 20 depicts an assembled cross-sectional view of exemplarycomponents provided in a medication injection pen according to a thirdexemplary embodiment of the present invention;

FIG. 21 depicts a view of a body provided in a medication injection penaccording to the third exemplary embodiment of the present invention;

FIG. 22 depicts a view of an insert provided in a medication injectionpen according to the third exemplary embodiment of the presentinvention;

FIG. 23 depicts a view of a driver provided in a medication injectionpen according to the third exemplary embodiment of the presentinvention;

FIG. 24 depicts a view of a dose set knob provided in a medicationinjection pen according to the third exemplary embodiment of the presentinvention; and

FIG. 25 depicts a view of a setback member provided in a medicationinjection pen according to the third exemplary embodiment of the presentinvention.

Throughout the drawings, like reference numerals will be understood torefer to like elements, features and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters exemplified in this description are provided to assist in acomprehensive understanding of exemplary embodiments of the presentdisclosure with reference to the accompanying drawing figures.Accordingly, those of ordinary skill in the art will recognize thatvarious changes to and modifications of the exemplary embodimentsdescribed herein can be made without departing from the scope and spiritof the claimed invention. Also, descriptions of well-known functions andconstructions are omitted for clarity and conciseness.

With reference to the drawing figures, particularly FIG. 1, a medicationinjection pen is shown and generally designated with the referencenumeral 10. The medication injection pen 10 may be used for theadministration of various medications, preferably liquid in nature,including but not limited to insulin and human growth hormone. The term“medication” is used in an illustrative and non-limiting manner to referto any substance that may be injected into a patient for any purpose.The medication injection pen 10 is provided for administering multipleinjections, the dose or volume of which may be set by the user and mayvary for each injection. Exemplary embodiments of medication injectionpen 10 of the present disclosure may be either disposable or reusablewhen the supply of medication therein has been exhausted.

With reference to FIGS. 2A and 2B, in an exemplary embodiment, themedication injection pen 10 generally includes a cap 12, a cartridgeholder 14, a spinner 16, a body 18, a dose knob 20, a setback member 22,a driver member 24, a leadscrew 26, a dose stop member 28, abi-directional click element 30, a leadscrew brake 32, and a push button34.

The cartridge holder 14 is formed to accommodate a medication cartridge36, which may be of any conventional design. By way of non-limitingexample, the cartridge 3 may include an elastomeric septum 38 at adistal end thereof, and an open proximal end 37 which exposes a slidableplunger 40. A medication is contained within the cartridge 36 betweenthe septum 38 and the plunger 40. As will be described in more detailbelow, the spinner 16 is configured to engage the plunger 40 and force adistal movement thereof to expel the medication from the cartridge 36.The spinner 16 includes an aperture formed to snap fit or otherwiseengage a distal end bead portion 27 (FIG. 7) of leadscrew 26 in mountingthe spinner 16 onto the leadscrew 26. A standard pen needle 11 (FIG. 2C)is used to administer medication from the medication injection pen 10.The needle is a double-ended cannula 5 which is threadedly mounted ontothreads 42 of the cartridge holder 14, as is well known in the an. Oneend of the cannula 5 is exposed for insertion into a patient, while thesecond end of the cannula is disposed to pierce the septum 38 of thecartridge 36. After administration of a set dose, the needle 11 may beremoved, in which case, the septum 38 may be self-sealing. The cap 12 isformed to releasably mount onto the cartridge holder 14, such as with asnap fit or other releasable engagement, to limit contamination of theseptum 38 and the surrounding portions of the cartridge holder 14. Aresilient holding arm 13 may extend from the cap 12 to provide a holdingforce for retaining the injection pen 10 in the user's pocket, purse, orcarrying case. One or more windows 15 may also be provided in thecartridge holder 14 to give a visual indication of the medication volumeremaining in the cartridge 36.

An exploded perspective view of a pen needle 11 of an exemplaryinjection pen is shown in FIG. 2C. The pen needle 11 includes the cover(outer shield) 1, an inner shield 2, a needle cannula 5 and a hub 3.During manufacture, a proximal end of the needle cannula 5 is insertedinto a center opening in the distal (patient) end 4 of the hub 3 until apredetermined length of the distal (patient) end of the needle cannula 5remains extended. The needle cannula 5 is secured by epoxy or adhesivein the distal end 4 of the hub 3. To protect users from injury and theneedle cannula 5 from being damaged, the inner shield 2 covers theexposed portion of the needle cannula 5. The open proximal end of theinner shield 2 is placed over the exposed portion of the needle cannula5. The open proximal end of the cover 1 envelops the inner shield 2,needle cannula 5, and hub 3. The distal end of the cover 1 is closed toprevent contamination and damage to the inner components of the penneedle 11, and to prevent injury to anyone who may handle it prior touse. When the user is ready to use the pen needle, the hub 3 is screwedonto threads 42 of cartridge holder 14 of the injection pen 10 (FIGS. 1,2A and 2B), and the cover 1 and shield 2 are separately removed from thehub 3/cannula 5 subassembly by a pulling action. The distal end of theinner shield 2 is closed to protect the user from an accidental needlestick by the needle cannula 5 after the cover 1 is removed. The innershield 2 is then removed to access the needle cannula 5.

With reference to FIGS. 3A and 3B, the body 18 is generally cylindrical,and includes a cylindrical partition or wall 30 extending across theinterior of the body 18 through which a channel 31 is formed comprisingan aperture 52. Cylindrical wall 50 effectively divides body 18 into twocompartments, a first compartment proximal to wall 50 for housing theplurality of dose setting and injecting components, as shown in FIGS. 2Aand 2B, and a second compartment distal of wall 50 for housing theleadscrew brake 32 and connecting to the cartridge holder 14. Thechannel 1 comprises internal threads 54 threadedly engagingcorresponding threads of the leadscrew 26. In an exemplary embodiment,the leadscrew 26 is provided with a non-circular cross-section, in whichcase, the aperture 52 is defined to allow rotational and thereby axialmovement of the leadscrew 26 therethrough. A plurality of second threads56 are provided on the interior of the body IS in the first compartmentand threadedly engaged with corresponding threads 62 provided on thedose set knob 20, as discussed further below. Body IX preferablyincludes a window 57 enabling the user to view a set dose indicated onthe outer surface of the dose set knob 20. As described further below, aseries of angled steps or teeth 55 are provided on the interior of thesecond compartment of body 18, circumferentially surrounding the distalend of channel 5. Teeth 55 are provided as part of a unidirectionalcoupling with the leadscrew brake 32 to allow the leadscrew 26 to rotatethrough the channel 51 in only one direction, that which causes theleadscrew to expel medication from cartridge 36. In an exemplaryembodiment, body 18 also includes a circumferential rib or groove 58onto which the cartridge holder 14 may be mounted with a snap fit.

With reference to FIGS. 4A and 4B, a generally cylindrical dose set knob20 with open proximal and distal ends is provided with an enlargedproximal portion or handle 60 defining a knob-like feature. Handle 60may include a plurality of grooves 61 enabling a user to securely griphandle 60 to set a dose of medication for an injection. Dose set knob 20includes at least one thread element 62 provided on its externalsurface, preferably near the distal end and threadedly engagingcorresponding threads 6 on the interior of body 18. An injection dose isset by the user by rotating dose set knob 20 in a predetermineddirection. Due to the threaded engagement with the body 18, rotation ofthe dose set knob 20 translates into axial movement of the dose set knobin the proximal direction extending away from and out of the body 18.Provided on the outer surface of body 18, area plurality of dosingindicia (not shown) indicating a set dose to be viewed through window 57provided on body 18.

A plurality of radially directed ridges 63 are providedcircumferentially along the interior surface of dose set knob 20adjacent to handle 60. Ridges 63 provide part of a clicking means inconjunction with an externally directed ratchet element 82 provided onclick arm 81 (FIG. 6A, 6B) of click element 30. Ridges 63 each comprisea sloped edge and a flat face for allowing relative rotational movementbetween the dose set knob 20 and click element 30 in only one directionin which the click arm 81 is enabled to slide over ridges 63, thusproviding an audible and tactile signal. Additionally, the proximaledges of ridges 63 define a proximally facing surface having a pluralityof teeth 64 disposed thereon. In an exemplary embodiment, teeth 64 areincluded as part of a clutch mechanism when engaged with correspondingteeth 74 (FIGS. 5A and 5B) disposed on setback member 22. When pressedtogether during injection, teeth 64 and 74 lock together, thuspreventing relative rotation between setback member 22 and dose set knob20, as further described below. Additionally, during dose setting, teeth64 provided on the dose set knob 20 function as a shelf, causing axialmovement of the setback member 74 together with the dose set knob 20, asthe dose set knob is rotated and moved axially out of the body 19. Doseset knob 20 also includes a plurality of longitudinally extending keysor splines 65 provided substantially along the interior surfacepreferably extending from the open distal end to the enlarged proximalportion 60. Longitudinal splines 65 engage with corresponding grooves 95provided on the exterior of dose stop member 28 to prevent relativerotation between the dose set knob 20 and the dose stop member 28, butto allow relative axial movement therebetween.

Setback member 22 comprises a generally cylindrical elongated member asshown in FIGS. 3A and 5B. Provided near the proximal end of setbackmember 22 are a plurality of ridges 73 spaced along the external surfacethereof. When the exemplary injection pen 10 is assembled, ridges 73 ofsetback member 22 face ridges 63 provided on the internal surface ofdose set knob 20. Ridges 73 include sloped edges and flat faces forengaging an internally directed ratchet element 84 provided on flexiblearm 83 of click element 34. As similarly described above, ridges 73enable relative rotational movement between the setback member 22 andclick element 30 in only one direction in which the internally directedratchet element 84 is enabled to slide over ridges 73 providing anaudible and tactile signal. The allowed direction of relative rotationbetween the setback member 22 and click element 30 is in the directionopposite that enabled by similar engagement between the dose set knob 20and the click element 30, so that the relative rotation between dose setknob 20 and setback member 22 is bi-directional.

Click element 30 is described with reference to FIGS. 6A and 6B. Asshown, click element 30 is a cylindrical tube like element comprising aplurality of radially flexible arms 81 and 83 oppositely disposed fromeach other. The click element 30 is preferably constructed with alongitudinal dimension similar to the length of the ridge portions 63,73 provided on the dose set knob 20 and setback member 22, respectively.Flexible arm 81 includes an externally directed ratchet element 82provided at the free end thereof facing ridges 63 provided on theinterior of dose set knob 20. Flexible arm 83, on the other band,includes an internally directed ratchet element 84 provided at the freeend thereof facing ridges 73 provided on the exterior of setback member22. During dose setting, click element 30 is permitted to rotaterelative to both the setback member 22 and dose set knob 20, but in onlyone direction with respect to each. In other words, during dose setting,click element 30 is rotationally locked to one of the setback member 22or the dose se knob 20 via flexible arms 83 and 81, respectively,depending on the direction of relative rotation for either normalsetting of a dose or dialing back of the set dose. When the dose setknob 20 is rotated in the direction in which ridges 63 are enabled toslide over the externally directed ratchet element 82 and produce anaudible signal, the click element 30 does not move rotationally relativeto the setback member 22 since such a movement is prevented by anengagement between click arm 83 and ridges 73. Conversely, when the doseset knob 20 is rotated in the opposite direction, the externallydirected ratchet element 82 engages with one of the ridges 63 causingthe click element to rotate together with the dose set knob 20. In thiscase, the internally directed ratchet element 84 is now permitted toslide past ridges 73 on the setback member, thereby producing an audiblesignal.

The exemplary construction of click element 30 described above allowsrelative rotation in both directions between the setback member 22 andthe dose set knob 20. Such a click element is not restricted to thedesign depicted in FIGS. 6A and 6B. Any similar element(s) enablingbi-rotational movement between setback member 22 and dose set knob 20,as described above, may be implemented in this embodiment, as would beevident to one of ordinary skill in the art.

As shown in FIG. 3A, setback member 22 includes an adapter element 71for snap-fitting with an internal cavity of push button 34. Push button34 is of any conventional design, but it is preferred that the snapengagement enables the push button to freely rotate on the adapterelement 71. Alternatively, push button 34 may be unitarily formed withthe adapter element 71. Additionally, as shown in FIG. 5B, a pluralityof longitudinally extending keys or splines 75 are provided along theinternal cylindrical surface of setback member 22. Splines 75 are formedto engage corresponding longitudinal grooves 85 provided on the externalsurface of driver member 24, shown in FIG. 7, thus preventing relativerotation between the setback member 22 and driver 24, while allowingrelative axial movement therebetween. With reference to FIG. 7, thedriver 24 includes open proximal and distal ends which provide a passage86 for leadscrew 26. In an exemplary embodiment, passage 86 comprises anon-circular cross-section corresponding to the non-circularcross-section of leadscrew 26, thus preventing relative rotationtherebetween. Driver 24 includes a disk 87 formed at the proximal endfor snap-engaging with at least one flexible tab 97 provided on theinterior surface of dose stop element 29 (FIG. A). With the snapengagement, the driver 24 is fixed axially relative to the dose stopelement 28, yet is able to rotate relative thereto. Driver 24 may alsoinclude one or more flexible legs 88 inwardly biased to engage leadscrew26. Flexible leg 88 may be provided to reduce any play between themating cross sections of leadscrew 26 and aperture 86 to improve doseaccuracy of the exemplary injection pen 10.

With reference to FIGS. 8A and 8B, a generally cylindrical dose stopelement 28 is provided for enabling last dose control so that a dosecannot be set or dialed up that is greater than the amount of medicationremaining in the cartridge 36, as further discussed below. Dose stopelement 28 includes a plurality of longitudinal grooves 95 on theexternal surface thereof. Grooves 95 engage with corresponding splines65 provided on the interior of dose set knob 20, thereby preventingrelative rotation therebetween, but allowing relative axial movement.Dose stop element 28 has an open proximal end 91 and open distal end 92,the distal end 92 preferably comprising a section of reduced diameter.Open distal end 92 defines a threaded opening with threads 93 disposedthereon for threadedly engaging corresponding threads 25 of theleadscrew 26 when assembled. Proximal end 91 defines a cavity housingsetback member 22, driver 24, and leadscrew 26. Flexible tabs 97 areprovided adjacent to the open distal end 92, extending into the interiorof the dose stop element 28. A recess 96 or cutout is provided in theexternal cylindrical wall of the dose stop element defining an area intowhich flexible tabs 97 are allowed to flex. During assembly, driver 24is inserted into the open proximal end 91, upon which disk 87 disposednear the distal end of driver 24 engages flexible tabs 97, and causesthem to flex outwardly into recess 9 until the disk 87 moves past theflexible tabs, at which time the flexible tabs 97 return to theirinitial positions to provide a blocking surface for the driver 24preventing relative axial movement therebetween.

While the above components are described as comprising specific featuresfor engaging and interconnecting other components of an exemplaryinjection pen, the above components are not limited to these specificfeatures. For instance, instead of the described mating non-circularcross-sections to prevent relative rotation between leadscrew 26 anddriver 24, one of ordinary skill in the art will appreciate that similarfunctionality may be provided using a spline/groove engagement forpreventing relative rotation therebetween while also allowing relativeaxial movement. Conversely, the above described spline/groove featuresmay be replaced with non-circular mating arrangements or other knownfeatures for preventing relative rotation while allowing relative axialmovement therebetween.

With reference to FIGS. 9A and 9B, leadscrew brake 32 comprises agenerally cylindrical housing portion 90 provided with a first diameterlarge enough to surround channel 51, as shown in FIG. 9B. Extending inthe distal direction, a pair of wall portions 92 is provided defining anaperture 93 with a non-circular cross-section to mate with thenon-circular cross section of leadscrew 26. Due to the matingnon-circular aperture 93, the leadscrew 26 is prevented from rotatingwith respect to the leadscrew brake. Further, the leadscrew brake 32comprises a pair of flexible ratchet arms 94 configured to engage thecylindrical ring of ratchet teeth 55 provided on the interior of thebody 18 to define a unidirectional coupling therebetween. Ratchet arms94 are configured to allow rotation of the leadscrew brake 32, andtherefore the leadscrew 26, in only one direction with respect to thebody 18. The allowed direction is that which causes the leadscrew 26 torotate through the threaded channel 51 in the distal direction to expelmedication. During injection, the leadscrew brake 32 rotates relative tobody 18, and ratchet arms 94 ride over the slanted or ramped portion ofteeth 55 to produce an audible clicking signal indicating the injectionis being performed. Rotation of the leadscrew brake in the oppositedirection causes the free ends of ratchet arms 94 to engage the flatfaces of teeth 55, which resist ratcheting of the ratchet arms 94 andthereby prevent relative rotation in this direction. Due to theunidirectional coupling between leadscrew brake 32 and teeth 55, anundesired rearward movement of the leadscrew 26 is prevented.

Having described exemplary structures, features and interrelationshipsbetween particular elements of the exemplary embodiment of medicationinjection pen 10 herein, the intended functionality of such an exemplarymedical pen device will now be described.

Following assembly of the exemplary elements as shown in FIGS. 2A, 2B,and as described above, to set a desired dose, the patient or user firstgrips and rotates the enlarged proximal end 60 of the dose set knob 20.The dose set knob 20 is rotated a number of rotations relative to thebody 18 until a desired dose is shown through the window 57 on the body18. Due to the threaded engagement of thread 62 on the dose set knob 20with the internal thread 56 of the body, the dose set knob is caused toscrew out of the proximal end of the body, carrying the setback member22 along with it by substantially the same distance. The dose stopmember 28 is also caused to rotate together with the dose set knob 20due to the spline/groove engagement between spline 65 provided on theinterior of the dose set knob 20 and groove 95 provided on the exteriorof dose stop 28. Rotation of the dose stop member 28 causes axialmovement of the dose stop member with respect to the body 18 in theproximal direction due to the threaded engagement between threads 93 onthe dose stop member and threads 25 of the leadscrew 26. The dose stopelement 28, however, moves a shorter distance axially than the dose setknob 20 due to a difference in the pitch of the thread 25 of theleadscrew 26 and the inner thread 56 of the body 18.

During normal dose setting for increasing a set dose, the leadscrew 26is prevented from rotating with respect to the body IS in the dosesetting direction due to the unidirectional coupling between theleadscrew brake 32 and the teeth 55 disposed on the body 18. Setbackmember 22 and driver 24, which are rotationally fixed to each other dueto spline/groove connection 75/85, are therefore also prevented fromrotating with respect to body 18 during dose setting, since the driveris rotationally fixed to the leadscrew via the mating of thenon-circular cross-section of leadscrew 26 and the non-circular aperture86 of the driver 24. Due to the snap it between disk 87 of the driver24, and flexible tabs 97 provided on the dose stop member 28, as thedose stop member screws out of the body in the proximal direction, thedriver 24 moves axially by the same distance, but does not rotate.

The setback member 22 is interconnected to the dose set knob 20 throughthe bi-directional click element 30. During normal dose setting, thedose set knob 20 rotates relative to the click element 30, and thus anaudible signal is provided due to the inner grooves 63 of the dose setknob 20 sliding past the externally directed ratchet element 82 onflexible arm 81. The externally directed ratchet element 2 tends toslide past ridges 63 in the dose setting direction because theinternally directed ratchet element 84 of flexible arm 83 is locked withthe ridges 73 provided on the setback member 22, which is prevented fromrotating in this direction due to its engagement with the driver 24 andleadscrew 26.

If the user initially sets a dose larger than desired, the set dose canbe “dialed back” or reduced by simply turning the dose set knob 20 inthe opposite direction. Rotation of the dose set knob 20 in this reversedirection, which is the direction of injection, would normally causerotation of the leadscrew 26 and thus axial movement of the leadscrewinto the cartridge 36. During injection, rotation of the leadscrew 26 iseffected due to the coupling between teeth 64 on the dose set knob andteeth 74 on the setback member 22, which is indirectly rotationallyfixed to the leadscrew 26. During dial back, however, the dose set knob20 and setback member 22 are not coupled via teeth 6474 and the dose setknob 20 rotates in this reverse direction relative to the setback member22 through the click element 30. Reverse rotation of the dose set knob20, during dial back, now causes the internal ridges 63 on the dose setknob 20 to engage and lock with the externally directed ratchet element82, forcing the click element 30 to rotate in this same direction. Theinternally directed ratchet element 84 is now caused to slide overridges 63 provided on the setback member 22, thereby producing anaudible signal indicating the dose is being reduced. Ratchet element 84tends to slide over ridges 73 in this direction since there is lessfriction provided between ratchet element 84 and ridges 73 than there isbetween the unidirectional coupling between the leadscrew brake 32 andthe body 18. In other words, the force required to dial back a set doseis not great enough to overcome the friction between the ratchet arms 94of leadscrew brake 32 and the teeth SS of body 1.

Once a desired dose is set, and the user desires to inject the set doseof medication, the medical injection pen 10 is applied to the skin ofthe patient to insert the needle cannula 5. The pen needle 11 isattached to the threaded portion 42 of the cartridge holder 14 prior toor after setting the desired dosage, as a matter of user preference.Once the pen needle 11 has been attached to the cartridge holder 14 andinserted into the patient, the push button 34 is depressed. The axialforce applied to the push button 34 by the user causes the teeth 74 onthe setback member 22 to engage with the teeth 64 on the dose set knob20 to mesh and rotationally lock the setback member 22 with the dose setknob 20, forming an injection coupling. The applied force causes thedose set knob 20 (due to a non self-locking threaded engagement with thebody 18 via threads 56 and 62) to rotate in the direction opposite thatwhich occurs during normal dose setting. This rotation is now impartedto the setback member 22 and therefore the driver 24 (due to thespline/groove connection 75, 85. Since the driver 24 mates with thenon-circular cross-section of the leadscrew 26, the leadscrew is alsocaused to rotate relative to body 19, which translates into axialmovement of the leadscrew into the cartridge 36 to expel a dose (due tothe threaded engagement between threads 25 on the leadscrew and threads54 disposed on channel 51 of the body 18). Axial movement of theleadscrew in the distal direction urges the spinner 16 against theplunger 40 to expel medication from the cartridge 32. The injectionforce is greater than the frictional force in the leadscrew brake 32,and hence the leadscrew brake allows rotation of the leadscrew 26 inthis direction during injection. As the leadscrew brake 32 rotates withthe leadscrew 26, oppositely disposed ratchet arms 94 slide over theteeth 55 disposed on the interior of body 18 to produce a clicking soundas the injection is carried out.

The dose administration process described above may be repeated untilthe medication in the cartridge 36 is spent. Prior to expelling the lastdose from the cartridge 36, it is desired to ensure that the last doseexpelled is consistent with the dose set by the user. In other words,the user should not be able to set a dose for an amount greater than theremaining volume of medication in the cartridge 36. This last dosecontrol is realized when threads 93 disposed on the dose stop element 28abut against a non-threaded portion of the leadscrew 26 at its proximalend, preventing further rotation of the dose stop member 28 on leadscrew26. When this occurs, the indicia on the dose set knob 20, read throughwindow 57, indicate the last remaining injectable volume of medicationin the cartridge 36. Once the dose stop member 28 is prevented fromrotating further, the dose set knob 20 is also prevented from furtherrotating in this direction for setting a larger dose, due to thespline/groove engagement 65/95 between dose set knob 20 and dose stopmember 28.

During dose setting, the dose stop member 28 changes its relativeposition on the leadscrew 26 based on the number of rotations of thedose set knob 20. Axial movement of the dose stop member 28 during dosesetting is by substantially the same distance as the leadscrew 26 movesinto cartridge 36 during injection. The length of axial movement ofleadscrew 26, and therefore the volume of medication to be expelled, isdetermined in part by the thread pitch of the leadscrew threads 25 andthreads 54 of the body, which is substantially the same as the pitch ofthe threads 93 of the dose stop member 28. Thus, the relative positionof the dose stop member 28 on the leadscrew 26 throughout administrationis indicative of the remaining dosage amount in the cartridge 36. Thedose stop member maintains its relative position on the leadscrew 26during injection due to its spline/groove engagement 6595 with the doseset knob 20. During injection, the dose sent knob 20, dose stop member28, setback member 22, driver 24 and leadscrew 26, are all rotationallylocked together. Since the threads 93 of the dose stop member 28 and thethreads 54 of the body 18 are of substantially the same pitch,simultaneous rotation of the dose stop member 28 and leadscrew 26results in the same axial movement. Thus, during injection, the dosestop member 28 does not move axially relative to leadscrew 26, andtherefore maintains its relative position with respect to the leadscrewas determined during the dose setting procedure. After administration ofthe last dose, if the injection pen 10 is reusable, the cartridge can bereplaced, whereas, if the pen is disposable, the entire pen 10 may bedisposed of.

As will be appreciated by those skilled in the art, variousmodifications can be made to the above exemplary embodiments withoutsubstantially altering the functionality of the injection pen 10. Forexample, such modifications may be made to ease the assembly of thevarious components, reduce the complexity of manufacturing, reduce thenumber of elements, or provide some additional improved functionality.Some such exemplary modifications are described below.

In one alternative embodiment, teeth 64 on the dose set knob 20,described above as part of an injection coupling with correspondingteeth 74 (FIGS. 5A and 5B) disposed on setback member 22, can generatedose setting click signals in the absence of click element 30. A springelement or wave washer with similar functionality may be provided tobias the teeth 74 of setback member 22 toward the corresponding teeth 64provided on the dose set knob 20, so that they are in constant meshedengagement. The spring force, however, is easily overcome by relativerotation between the dose set knob 20 and setback member 22, whichcauses the corresponding teeth 64/74 to slip over each other producingan audible and tactile signal.

In another exemplary embodiment, an alternate injection coupling isprovided between a modified dose set knob 20 (teeth 64 removed) and amodified setback member 22′, shown in FIG. 10. In this embodiment, theinjection coupling described above with respect to teeth 64 on the doseset knob 20 and corresponding teeth 74 on the setback member 22, isreplaced by an extended surface 101 provided near the proximal end ofthe setback member 22′ the extended surface 101 being defined by alarger diameter with respect to ridges 73. Click element 30 includes afirst surface 102 positioned co-axially on and surrounding the extendedsurface 101. During the dose setting operation, click element 30 ispositioned on setback member 22′, such that click arms 81 and 83 arefree to flex and slide past ridges 73 and 63, respectively. In thisembodiment, the dose setting and dial back mechanism is unchanged.During injection, however, upon the user applying an injection force topush button 34, the setback member 22′ is pushed into the dose set knob20 and into click element 30. As the setback member 22 moves axiallytoward click element 30, the extended surface 101 is moved intoengagement with click arm 83, as shown in FIG. 108. In this position,click arm 83 is prevented from flexing radially inward to slide pastgrooves 63 in the dose set knob, thus locking click element 30 to doseset knob 20. Relative rotation of the dose set knob 20 with respect tothe setback member 22′ in this direction during dose setting would haveenabled the ratchet arm 83 to ride over ridges 63 to reduce a set dose.During injection, however, ratchet arm 83 is now prevented from flexingaway from ridges 63, and thus prevented from sliding over ridges 63, bythe blocking engagement of extended surface 101. Accordingly, thesetback member 22′ is now rotationally locked to dose set knob 20 vianon-sliding engagement with ratchet arm 83, thus enabling injection of aset dose, as described above.

In another embodiment, the exemplary injection pen 10 is modified tofacilitate the manufacture of injection pens providing different dosingneeds. For example, an injection pen for administering a firstmedication may desire liner dosing intervals for more precise dosagecontrol than that of another medication. To utilize the same dosesetting and injection functionality of the exemplary injection pendescribed above, it is desired to be able to provide a plurality of pensmeeting the various dosing needs with greater compatibility, so as toreduce the complexity of manufacturing multiple such pens.

One such modification is made to the embodiment illustrated in FIG. 9Bto switch the ratchet arms 94 provided on the leadscrew brake 32 withthe ratchet teeth 55 provided on body 18, as shown in FIG. 11A. Asshown, the body 18′ now includes ratchet arms 111 and the leadscrewbrake 32′ now includes teeth 112. Engagement between ratchet arms 111and teeth 112 serves to provide similar unidirectional functionality asdescribed in the previous embodiment. Leadscrew brake 32′ in thisalternative embodiment facilitates a change in a desired injection clickinterval necessitated by a desired change in a dosing interval. Forexample, the injection clicks realized by relative rotation of theleadscrew brake 32 preferably correspond to a dose increment, and arerelated to the spacing of the teeth 112. If the dose increment ischanged to have a greater or smaller interval, a leadscrew brake with acorresponding spacing of teeth 112 is assembled in the injection pen asshown, as opposed to providing a new body 18 with the desired spacing ofteeth 55, as in the earlier embodiment. The smaller leadscrew brake 32is easier and less costly to manufacture than the body 18, and hence itis advantageous to replace leadscrew brake 32 in the modified injectionpen as opposed to replacing the body 18.

A further modification, shown in FIGS. 11B-11F, enables an easier changeof the thread pitch of the leadscrew if desired to increase or decreasea dose rate. For example, the threads 25 of the leadscrew 26 may bemodified to include a larger pitch, so that the same number of rotationsof the leadscrew results in greater axial movement of the leadscrew intocartridge 36 and therefore a larger dose volume. In the previousembodiment, if the threads 25 of the leadscrew 26 are modified, thethreads 54 of the body are also modified accordingly. The additionalmodification shown in FIG. 11B provides an insert 114 which replaces thefeatures of the partitioning wall 50 and channel 51 with threads 54disposed thereon of the exemplary embodiment (see FIG. 3A). Insert 114is a nut-like element with ratchet arms 115 disposed thereon. Insert 114comprises a wall 118 with an aperture 119 therethrough. Aperture 119 isdefined by a cylindrical channel 116 with threads 117 disposed on theinterior thereof. Body 18″ now includes a shelf or ledge 121 forming acontact surface engaging with a proximal surface of insert 114 todetermine axial placement of the insert 114 into body 18″. Shelf 121comprises at least one protrusion member 122 configured to engaged acorresponding recess 120 on the proximal face of insert 114. Engagementbetween protrusion 122 and recess 120 prohibits relative rotationalmovement between insert 114 and body 18″ Alternatively, any similarkey/groove type structure may be provided to limit relative rotationalmovement between insert 114 and body 18″.

Insert 114 may also be provided with an additional molded spring feature124 to maintain the positioning of insert 114 against shelf 121 in body18″ Molded spring feature 124 also presses against cartridge 36, asshown in FIG. 11F, to prevent the cartridge from moving when the needle5 is inserted into the cartridge septum 38 prior to injection. Thisfeature provides greater accuracy in dose injection and preventsundesired wasting of medication, in prior art injection pens, thecartridge may be allowed to move a slight distance in the proximaldirection during this operation, resulting a small waste or “drool” ofthe medication.

In another exemplary embodiment, an end of injection click or signal isprovided by a modified dose set knob 20′ including a radially flexibleleg 128 near the distal end of dose set knob 20′ extending in the distaldirection. Flexible leg 128 interacts with an angled protrusion 130,shown in FIG. 12B, disposed on a proximal surface of partitioning wall50 of the body 18. Angled protrusion 130 is preferably fixed topartitioning wall 50 at only one end, which is the end spaced fartheraway from the internal surface of body 18. At a zero dose position, whenthe dose set knob 20′ abuts partitioning wall 50, flexible leg 128 ispositioned near protrusion 130, but not in touching engagement. Uponsetting of a desired dose, as the dose set knob 20′ is rotated, flexibleleg 128 moves between the angled protrusion 130 and an internal surfaceof body 18, as shown in FIG. 12C. Since the angled protrusion 130 is notfixed to the partitioning wall 50 at the end closest to the internalsurface of the body 18, the angled protrusion flexes radially to allowpassage of the flexible leg therebetween and reduce the friction forinitially overcoming the protrusion during dose setting. Once flexibleleg 128 passes behind protrusion 130, continued rotation of the dose setknob 20′ will result in axial movement of the dose set knob away frompartitioning wall 50 so that the flexible leg 128 no longer interactswith protrusion 130. Normal setting of the dose is now performed.

As the set dose is injected, dose set knob 20′ screws back into body 18and moves toward partitioning wall 50. As the injection is nearing itsend, flexible leg 128 once again engages protrusion 130 as shown in FIG.12E. This time, as flexible leg 128 abuts against protrusion 130, it isnot allowed to pass between the protrusion 130 and the internal surfaceof body 18. Now, the flexible leg 128 is caused to flex radially inwardto slide past protrusion 130 until it moves past the end of protrusion130, at which time flexible leg 128 snaps against the internal surfaceof body 18 providing an audible and tactile signal. At this point, theset dose is completely delivered and the injection pen is at a zero doseposition.

In one embodiment, an end of dose click may be provided as a distinctsignal distinguishable from the injection clicks provided by theleadscrew brake 32 as discussed above with respect to FIG. 9. In anotherembodiment, however, the injection clicks are muted, and a user sensesonly the end of injection click provided between the flexible leg 128and protrusion 130. One way to mute the injection clicks is to replaceratchet teeth 55 provided on the body 18 with a rubber like ring orbrake 134, as shown in FIG. 13. During injection, the leadscrew brake 32still rotates with respect to body 18, but in this embodiment ratchetarms 94 slide along the surface of the rubber brake 134 withoutproviding an audible or tactile signal. Rubber brake 134 is fixed to thebody 18 using an adhesive or other structure, so that it does not rotaterelative to the body 18, and therefore is still capable of functioningas a unidirectional coupling with leadscrew brake 32. Ratchet arms 94 ofthe leadscrew brake 32 are preferably beveled or otherwise configured togrip the rubber brake 134 to prevent relative rotation therebetween,similar to the embodiment discussed in FIG. 9B. Additionally, one ofordinary skill in the art will appreciate that rubber brake 134 may bemodified as similarly discussed in FIGS. 11A and 11B.

In another exemplary embodiment, an element or elements are added toimprove the mechanical efficiency of an exemplary injection pen 10, byeliminating or reducing the friction between elements rotating relativeto each other or those moving axially with respect to each other. Oneparticular engagement with undesirable friction is between the pushbutton 34 and the adapter element 71 provided on the setback member.During dose setting and injection, push button 34 preferably rotatesfreely on adapter element 71. In an exemplary embodiment, as partlyshown in FIG. M, adapter element 71 includes a point 77 provided at thecenter of the axis of rotation of the setback element 22. This point 77contacts push button 34 near its center of rotation. Providing such acontact surface between these elements at or near the center of rotationreduces frictional torque between these elements during relativerotation, and thereby increases efficiency. To further reduce thefriction between setback member 22 and push button 34, one embodimentincludes at least one rolling ball (i.e. ball bearing) 140 situatedbetween an internal surface of the push button 34 and a surface of theadapter element 71, as shown in FIG. 14A. Rolling balls 140 function totranslate sliding friction between engaging elements into a reducedrolling friction. In another embodiment, shown in FIG. 148, a pair ofmagnets 142 a and 142 b with the same polarity are provided on adjacentcontact surfaces facing each other. For instance, a first magnet 142 ais provided on the interior of push button 34, whereas the second magnet142 b is provided on a contact surface of adapter element 71 facing thefirst magnet. Due to the same polarity between magnets 142 a and 142 b,the resulting repulsion force reduces the contact force between thesetwo surfaces, thus reducing friction therebetween without affecting thepush force required for injecting medication. One of ordinary skill inthe an will appreciate that the above methods may also be implemented incombination. Further, such methods may be implemented between any twocomponents with a linear or rotational contact surface, to furtherimprove mechanical efficiency.

The exemplary embodiments described above may be provided as a reusableor disposable pen. In a disposable implementation, cartridge holder 14and body 18 are preferably irreversibly assembled. In one embodiment, asdescribed with respect to FIG. 3A, a circumferential rib provided on thecartridge holder 14 snaps into engagement with a groove 58 on body. Inanother embodiment, shown in FIG. 1A, threaded insert 114 may include atleast one tab 125 for snap-fitting with a recess 126 provided oncartridge holder 114. Since threaded insert 114, as discussed withrespect to FIGS. 11B and 11C, is fixed both axially and rotationally tobody 18, snap-engagement of the cartridge holder 14 to threaded insert114 prevents relative rotation between the cartridge holder and thebody.

In a preferred embodiment shown in FIG. 158, cartridge holder 14 andbody 18 comprise a set of threads 151 and 152 which provide a securethreaded coupling between the cartridge holder 14 and body 18.Additionally, one of the cartridge holder and the body comprises a snap154 and the other comprise a recess 156 for engaging snap 154. Thesnap/recess engagement is preferably a one-way radial snap. Thus, oncethe body 18 and the cartridge holder 14 are screwed together, the snap154 moves into engagement with recess 156 until they snap togetherproviding a secure, irreversible connection, with minimal or no playbetween the cartridge holder 14 and body IN, thereby increasing accuracyof the dose injection and reducing/eliminating unnecessary waste ofmedication.

In view of the above description, another exemplary embodimentcomprising similar components and functionality is shown in FIGS. 16Aand 168. The components shown in FIGS. 16A and 168 have similarfunctionality to those described above, unless noted otherwise, andtherefore their detailed description is omitted herein, in thisembodiment, body 218 is similar to the body 18″ shown in FIGS. 11B and11D. A first compartment defined by the interior of body 218, proximalto wall 250, houses a dose set knob 220, a setback member 222, a dosestop member 228, a driver 224, and a leadscrew 226. The secondcompartment defined by the interior of body 218, distal to wall 250,houses a threaded drive insert 233 and a distal end 225 of driver 224.Wall 250 is provided with an aperture sized to fit the main cylindricalbody of driver 224, but not the enlarged distal end 225, as shown inFIG. 16B, thus axially fixing the driver 224 to the body 218.

In this embodiment, the leadscrew 226 has a circular cross-section, andis rotatably fixed to driver 224 via a key/groove engagement as shown inFIG. 17. A proximal end of leadscrew 226 includes keys 217 engaging inlongitudinal grooves 223 provided on the interior of driver 224. Viathis key/groove engagement, the leadscrew 226 is rotationally fixed tothe driver 224 but is allowed to move axially relative thereto. Driver224 comprises longitudinal grooves 285 engaging internal keys or splines275 provided on the interior of setback member 222 to rotationally lockthe driver 224 thereto. Driver 224 now includes an enlarged distal end225 provided with a ring of teeth 255 circumferentially disposed thereonand functioning similarly to the toothed leadscrew brake 32′ in FIGS.11A and 11B. Distal end 225 comprises part of a unidirectional couplingalong with the threaded insert 233, as similarly discussed above withrespect to FIGS. 9B and 11B. Threaded insert 233 comprises an aperturewith threads disposed thereon, which are threadedly coupled tocorresponding threads on leadscrew 226, similar to insert 114 of FIG.11C.

In this embodiment, last dose control is provided by a modified dosestop member 228, as shown in FIG. 18. Dose stop member 228 comprises aring link structure provided with a series of threads 290 disposed onthe exterior surface thereof and threadedly engaged to threads 291disposed on the dose set knob 220. Dose stop member 228 is rotationallyfixed to setback member 222 via corresponding ridges 272 provided on theinterior surface of dose stop member 228, which mesh with similar ridges273 disposed on the setback member, as shown. In this embodiment, as thedose set knob 220 is rotated to set a desired dose or decrease atoo-large dose, dose stop member 228 screws into threads 291 disposed onthe dose set knob by an amount related to the set dose. Duringinjection, the dose stop member 228 maintains its relative position withrespect to threads 291, since the setback member 228 is rotationallyfixed to the dose set knob 220. Therefore, dose stop member 228 and doseset knob 220 rotate together and there is no relative movementtherebetween. Once the dose stop member 228 screws into the end threadof the threads 291, it is prevented from rotating further, and thusfurther rotation of the dose set knob to set a larger dose is alsoprevented. Such an occurrence indicates a final dose of medicationremaining in the cartridge.

To set a desired dose for injection the user rotates the dose set knob220. Audible clicking of the set dose is provided by slipping of teeth264 on dose set knob 220 with teeth 274 on setback member 222, assimilarly described in the previous embodiment above. Teeth 264 and 274are held in meshed engagement by a spring element 233 provided withinpush button 234. Similar to the previous embodiment, when the userpresses push button 234 to inject a dose, the setback member 222 isrotationally locked to the dose set knob 220 via engagement between theteeth 264 and 274. Setback member 222 now rotates with dose set knob220, as the dose set knob screws back into body 21. Rotation of thesetback member 222 translates to driver 224 which rotates the leadscrew226. The leadscrew 224 rotates through the fixed threaded drive insert233 and into the cartridge to expel a dose. As the driver 225 rotates inthis direction, the distal ring of teeth 255 provides the injectionclicking as teeth 255 slip past ratchet arms disposed on threaded driveinsert 233.

In another embodiment, last dose control is similarly provided with amodified dose stop element 328, as shown in FIG. 19A. Dose stop element328 is a half-nut like member with a series of threads disposed on theinternal surface thereof, threadedly engaging threads 332 provided onthreaded setback member 322. Dose set knob 320 comprises twolongitudinally extending ribs or splines 330, circumferentially spacedfrom each other by a distance substantially the same as the length ofthe dose stop element 328. Splines 330 engage corresponding edges ofdose stop element 328 to rotationally lock the dose stop element to thedose set knob 320. During setting of a dose, dose stop member 329 screwsonto threads 332 of setback member 322, its relative position indicatedthe remaining volume of medication in the cartridge. When the dose stopmember 329 reaches an end of thread 332 or a fixed stop on either thedose set knob 320 or setback member 322, dose stop element 328 isprevented from rotating further and thus limiting the dose to thatremaining in the cartridge.

Yet another embodiment, using a similar principle of operation, is shownin FIG. 19B. In this embodiment, dose stop element 428 is threaded alongits outer surface with threads 427. The inner surface of dose set knob420 is provided with at least one thread disposed thereon with a lengthsufficient to maintain constant engagement with threads 427 of dose stopmember 428. Setback member 422 comprises two longitudinally extendingribs or splines 430, circumferentially spaced from each other by adistance substantially the same as the length of the dose stop element428. Splines 430 engage corresponding edges of dose stop element 428 torotationally lock the dose stop element to the setback member 422. Theouter surface of the setback member 422 in this embodiment is providedwith a substantially smooth surface to enable axial movement of dosestop element 428 thereon. In this embodiment, the last dose volume isthat indicated when dose stop element 428 is prevented from moving anyfarther axially with respect to setback member 422. Axial movement ofdose stop element 428 is prevented when a first edge of element 428abuts a fixed stop in the dose set knob 420 or on the setback member422.

In view of the above description, yet another exemplary embodiment of aninjection pen comprising similar functionality is shown in FIG. 20. Asshown in the cross-sectional view, an exemplary injection pen in thisembodiment comprises a main body 518, a dose set knob 320, a setbackmember 522, a driver 524, a leadscrew 526, a dose stop member 528, andan insert 530. The body 518 is modified as shown in FIG. 21. As shown,at least one ratchet arm 555, attached at one end of a sidewall or thebody 18 distal to the partitioning wall 550, is internally directed andpreferably provided with series of ridges or teeth 557 at the free endthereof. Teeth 557 engage with teeth 595 disposed on the outer surfaceof insert 530, as shown in FIG. 22. Teeth 557 are forced into engagementwith teeth 595 on the insert 530 when a cartridge holder is attached tobody 18, due to the cartridge holder engaging protrusion 559 provided onthe outer surface of ratchet arm 555. When the cartridge holder isattached to the body 518, the insert 530 is prevented from rotating ineither direction due to the forced toothed engagement. When thecartridge holder is removed, such as to re-use the injection pen, theratchet arms 555 are free to ratchet and enable relative rotationbetween the insert 530 and the body 518, to reload the leadscrew forsubsequent use of the injection pen. The insert 530 comprises anaperture 531 with a non-circular cross-section for mating a similarnon-circular cross-section of the leadscrew, to prevent relativerotation therebetween. A plurality of teeth 556 are providedcircumferentially along an internal surface of the body 518 proximal tothe partitioning wall 550. Teeth 56 serve to engage a ratchet element586 provided near a distal end of driver 524, as shown in FIG. 23described further below.

As shown in FIG. 23, driver 524 comprises an elongated cylindricalmember with open distal and proximal ends for allowing passage of theleadscrew 526 therethrough. Driver 524 includes a plurality of splines583 provided near the proximal end for engaging corresponding grooves onthe interior of setback member 522 for rotationally coupling the driver524 and setback member 522 together. A pair of protrusions 585 isprovided near the distal end of driver 524 for snap-engaging with thebody 518 behind partitioning wall 550. This snap-engagement prohibitsrelative axial movement between the driver 524 and the body 518 whileallowing relative rotational movement therebetween. Driver 524 includesat least one thread element 582 provided on the interior surface forthreadedly engaging with a corresponding thread of the leadscrew 526. Asdiscussed further below, it is this thread engagement that forces theleadscrew 526 to move axially in the distal direction to inject a setdose.

As shown in FIG. 24, the dose set knob 520 is an elongated cylindricalmember provided with an outer thread 562 threadedly engaging an internalthread of the dose set knob, similar to the above embodiments. In thisembodiment, the dose set knob 520 comprises at least one ratchet arm 564provided near the distal end thereof, for engaging a plurality of ridges573 provided on the outer surface of the setback member 522, as shown inFIG. 25. The ratchet arm 564 includes a rounded protrusion 565 forenabling slipping of the ratchet element in both directions over ridges573 provided on setback member 522, to provide audible click signalsduring both normal dose setting and dial-back. Dose set knob 520 alsoincludes a plurality of teeth 563 provided circumferentially along aninternal surface of the dose set knob, as shown. During dose setting,teeth 563 are situated in the recess 576 on the outer surface of thesetback member, as shown in FIG. 25. The teeth 563, in this embodiment,serve as an injection coupling to rotationally lock the dose set knob524) to the setback member 522. In another embodiment, the injectioncoupling may be between a set of engaging teeth provided on the setbackmember 522 and the dose set knob 520, as similarly discussed withrespect to the first embodiment shown in FIGS. 4A and 5A (teeth 64 and74). Dose set knob 520 comprises a plurality of threads 591 providedalong the internal surface thereof for threadedly engaging with threads590 of the dose stop member 528.

Having described exemplary structures, features and interrelationshipsbetween the particular elements of FIGS. 20-25, the intendedfunctionality of such an exemplary injection pen will now be described.Discussion of particular elements and features similar to the aboveembodiments, have been omitted herein.

To set a desired dose for injection, a user rotates the dose set knob520 in a first direction. Relative rotation between the dose set knob520 and the setback member 322 produces a series of dose-setting clicksdue to the engagement between ridges 573 and ratchet elements 564, 65.If a too-large dose is set by the user, the user can rotate the dose setknob 320 in a second, opposite direction to dial back the set dose.During dose setting, the dose set knob is free to rotate in both thefirst and second direction with respect to the setback member 522. Toinject a set dose, the user presses a push button 34, which pushes thesetback member 522 in the distal direction and causes ridges 573 on thesetback member to engage teeth 563 provided on the dose set knob. Thedose set knob 520 and the setback member 522 are now rotationally fixedwith respect to each other. Now, as the dose set knob rotates back intothe body 518, the setback member 522 is also caused to rotate whichforces driver 524 to rotate therewith. The leadscrew is prevented fromrotating with respect to body 518 due to its mating engagement with theinsert 530, which is rotationally fixed to the body 518 when thecartridge holder is attached to the body 518, as described above. Sincethe leadscrew 526 is rotationally fixed, relative rotation between thedriver 524 and the leadscrew 526 causes the leadscrew 526 to moveaxially into the cartridge to inject a set dose, due to its threadedengagement with threads 582 provided on the driver 524. Duringinjection, as the driver 524 rotates relative to body 518, ratchet arms586 provide an injection click signal as they ride over teeth 556provided on the interior of body 518. In this embodiment, last dosecontrol is performed similarly to that described above with respect toFIG. 18, to prevent a user from setting a dose larger than a remainingvolume of medication remaining in the cartridge.

While the present invention has been shown and described with referenceto particular illustrative embodiments, it is not to be restricted bythe exemplary embodiments but only by the appended claims and theirequivalents. It is to be appreciated that those skilled in the art canchange or modify the exemplary embodiments without departing from thescope and spirit of the present invention.

1. A medication injection pen comprising: a housing; a dose set knobcomprising at least one internal thread and being rotatable with respectto said housing to set a desired injection dose; a leadscrew providedwith a thread element and advanceable in a first direction, said firstdirection being that which expels medication from a cartridge; a driverselectively rotatable with said dose set knob to rotate said leadscrewand advance said leadscrew in said first direction; a setback memberrotationally fixed to said driver for preventing relative rotationtherebetween; and a dose stop member engaged with said dose set knob,wherein movement of said dose stop member with respect to said dose setknob limits a user from setting a dose that is greater than aninjectable volume of medication remaining in the cartridge.
 2. Themedication injection pen according to claim 1, wherein said dose stopmember is rotationally movable with respect to said dose set knob whensaid dose set knob is rotated relative to said setback member, and saiddose stop member is rotationally coupled to the setback member.
 3. Themedication injection pen according to claim 2, wherein said dose stopmember comprises a partial nut situated on said setback member between apair of longitudinally extending ribs provided on said setback member.4. The medication injection pen according to claim 2, wherein said dosestop member is rotationally coupled to the setback member via engagementbetween corresponding ridges provided on an internal surface of saiddose stop member and an external surface of said setback member.
 5. Themedication injection pen according to claim 4, wherein said dose stopmember comprises a ring link structure situated on said setback member.6. The medication injection pen according to claim 1, wherein the axialmovement of said dose stop member is limited when a first edge of thedose stop member abuts a fixed stop on said dose set knob or on saidsetback member.
 7. The medication injection pen according to claim 1,wherein said dose stop member is rotationally coupled to said dose setknob, and said dose stop member is rotationally movable with respect tosaid setback member when said dose set knob is rotated relative to saidsetback member.
 8. The medication injection pen according to claim 7,wherein said dose stop member comprises a partial nut including internalthreads engaging an external thread of said setback member.
 9. Themedication injection pen according to claim 7, wherein said does setknob comprises two longitudinally extending ribs engaging correspondingedges of said dose stop element to rotationally couple said dose stopelement to said dose set knob.
 10. The medication injection penaccording to claim 1, further comprising: a click element positionedbetween said dose set knob and said setback member, said click elementcomprising a first arm member engaging an internal surface of said doseset knob, and a second arm member engaging an external surface of saidsetback member, wherein one of the said first and second arms producesan audible signal when said dose set knob is rotated with respect tosaid housing.
 11. The medication injection pen according to claim 10,wherein said internal surface of said dose set knob and said externalsurface of said setback member, each comprise a plurality of teeth, andone of said first and second arms slides over ridges of said pluralityof teeth of said setback member or ridges of said plurality of teeth ofsaid dose set knob to produce the audible signal at each ridge.
 12. Themedication injection pen according to claim 11, wherein said pluralityof teeth of said dose set knob are configured to allow relative rotationbetween said dose set knob and said click element in a second rotationaldirection, and said plurality of teeth of said setback member areconfigured to allow relative rotation between said setback member andsaid click element in an opposite direction to the second rotationaldirection.
 13. The medication injection pen according to claim 12,wherein when said dose set knob rotates relative to said click elementin said second rotational direction, said first arm produces the audiblesignal, and when said setback member rotates relative to said clickelement in said opposite direction to said second rotational direction,said second arm produces the audible signal.
 14. The medicationinjection pen according to claim 1, wherein said housing furthercomprises a flexible protrusion provided on a surface within saidhousing, and said dose set knob further comprises a flexible tab elementwhich engages said protrusion to produce an audible signal uponcompletion of injection of a set dose.
 15. The medication injection penaccording to claim 14, wherein when said dose set knob rotates relativeto said housing to set a desired injection dose, said flexible tabelement passes between a first edge of said protrusion and a sidewall ofthe housing, causing said protrusion to flex away from said sidewall.16. The medication injection pen according to claim 15, wherein saiddose set knob rotates in an opposite direction to inject a dose, and inthis direction, said flexible tab element engages a second edge of saidprotrusion causing said flexible tab element to flex radially inward,wherein once said flexible tab element passes an end of said protrusion,said flexible tab element returns to an initial position while providingan audible signal indicating an end of injection.
 17. The medicationinjection pen according to claim 14, wherein the housing includes achannel having internal threads that threadedly engage the threadelement of said leadscrew; said channel includes a wall disposed on atop surface of said channel; and, said flexible protrusion is disposedon said wall of said channel.